1. Field of the Invention
The invention relates to a digital audio signal playback apparatus, more particularly to a digital audio signal playback apparatus with a scratch effect control device.
2. Description of the Related Art
FIG. 1 illustrates a conventional digital audio signal playback apparatus 1, which disclosed in U.S. Pat. No. 6,535,462, that includes a disc carrier 11 to be loaded with an optical disc (not shown), such as a compact disc, a laser pick-up head 12 for reading digital audio data recorded in the optical disc, a circuit unit 13 coupled electrically to the disc carrier 11 and the laser pick-up head 12, a control panel 14 coupled electrically to the circuit unit 13 for turntable control, a turntable unit 15 driven by a driving device 17 that is coupled electrically to the circuit unit 13, and a pick-up device 16 coupled electrically to the circuit unit 13 and interacting with the turntable unit so as to generate a control signal representative of angular velocity of the turntable unit 15.
The circuit unit 13 generally includes a high-frequency amplifier, a drive integrated circuit, a digital signal processor, a system microprocessor, DRAMs, a digital-to-analog converter, a low-pass filter, etc. The circuit unit 13 stores the digital audio data recorded in the optical disc, which is disposed on the disc carrier 11, and read by the laser pick-up head 12 in the DRAMs. At the same time, a disc jockey inputs control parameters via the control panel 14 to set angular velocity and rotation direction of the turntable unit 15. The circuit unit 13 then controls the driving device 17 to drive the turntable unit 15 to rotate in accordance with the control parameters such that the pick-up device 16 subsequently generates the control signal representative of angular velocity of the turntable unit 15. Finally, the circuit unit 13 controls output of the digital audio data stored in the DRAMs in accordance with the control signal from the pick-up device 16 so as to impart a scratch effect to the digital audio data.
The turntable unit 15 can be one of two types. As shown in FIG. 2, the turntable unit 15 may be one that includes a platter member 151, and a light-reflecting member 152 adhered on the platter member 151 and formed with a set of light-reflecting marks 153 which serves as a pick-up pattern, and which are arranged at a periphery of the light-reflecting member 152. However, the exposed light-reflecting member 152 easily peels away from the platter member 151 after a period of use, thereby necessitating frequent replacement of the turntable unit 15.
Referring to FIG. 3, another type of the turntable unit 15′ is shown to include a lower platter member 151′, an upper platter member 153′ superposed on the lower platter member 151′ and formed with a set of through holes 155 at a periphery thereof to serve as a pick-up pattern, and a light-reflecting interlayer 154 interposed between the lower and upper platter members 151′, 153′. The pick-up device 16 interacts with the pick-up pattern so as to generate the control signal representative of the angular velocity of the turntable unit 15′. However, dust easily accumulates in the through holes 155 such that a desired scratch effect cannot be imparted to the digital audio data.